<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>

    <style>
        /* .topbox {
            width: 900px;
            height: 50px;
            border: 1px dashed red;
            margin: 20px auto;
        }

        .bannerbox {
            width: 900px;
            height: 200px;
            border: 1px dashed red;
            margin: 20px auto;
        } */

        .box {
            width: 900px;
            background-color: #eee;
            border: 1px dashed #ccc;
            margin: 0px auto;
        }
        .top {
            height: 80px;
        }
        .banner {
            height: 120px;
            margin: 5px auto;
        }
        .main {
            height: 500px;
        }

        .bottom {
            height: 120px;
            margin: 5px auto;
        }
    </style>
</head>
<body>
    <div class="top box">top</div>
    <div class="banner box">banner</div>
    <div class="main box"></div>
    <div class="bottom box"></div>
</body>
</html>